Wireless networks and systems are becoming increasingly popular. Wireless communications, however, are constrained due to a limited amount of available, interference free spectrum that may be used for reliable communications within a geographic area.
To enhance the availability and reliability of interference free spectrum, procedures that are governed by regulatory agencies (e.g., the Federal Communications Commission (FCC) in the United States) have been developed for allocating and governing spectrum use. In the U.S., for example, the FCC licenses spectrum in a primary spectrum market to Commission licensees. A secondary market exists for the Commission licensees to sublease spectrum for use by other parties. An entity that seeks to transfer spectrum in the secondary market commonly is referred to as a “spectrum provider” or a “spectrum holder,” and an entity or wireless communications system or device that has a need for spectrum to carry out wireless communications commonly is referred to as a “spectrum user.” A spectrum provider or holder also may be a spectrum user.
In the U.S., some spectrum may be used without a license, but regulations on the spectrum may be imposed. For example, the FCC has implemented the elimination of analog television (TV) broadcasts in favor of digital TV broadcasts. This has freed up spectrum channels for use by unlicensed radio systems to offer various services, such as mobile communications and Internet access. This freed spectrum is commonly referred to as TV whitespace (TVWS), which is made up of the guard bands and unused TV channels between channel 2 and channel 51 (corresponding to 54 MHz to 698 MHz).
To avoid interference with digital TV broadcasts and other incumbent systems, such as wireless microphone systems, radios that use the TV whitespace are required to register and receive a channel map of available channels that may be used for the communications activity of the radio system. Current regulations require these radio systems to register every twenty-four hours. Also, for mobile radios, if the radio moves into a new location, a new registration is required. Other regulations on the radios are present, such as transmitted power limits for different types of radios. Additional information regarding the regulation of TV whitespace may be found in FCC 08-260, Second Report and Order and Memorandum Opinion and Order, Adopted Nov. 4, 2008 and Released Nov. 14, 2008, the entirety of which is incorporated herein by reference. Similar proposals have been made in places other than the United States. For example, Ofcom in the United Kingdom has described access to certain spectrum by cognitive radios in “Digital Dividend: Cognitive—Access Consultation on License-Exempting Cognitive Devices Using Interleaved Spectrum,” published Feb. 16, 2009.
Conventional wireless networks use radios that transmit or receive communications within a fixed channel set or band. In some circumstances, radios are permitted to search among a predefined set of channels in a programmed way, as in trunked radio or cellular networks. The pool of available spectrum, however, is typically finite (or static), and radio channels and bandwidth are not optimized on an individual user or application basis. This leads to high inefficiencies in spectrum utilization, and since spectrum is a scarce resource, less than optimal performance for the user and network as a whole can occur.
To allocate spectrum efficiently and on a non-interfering basis, spectrum should be described in terms that render spectrum tantamount to a fungible asset. In this manner, “chunks” or “portions” of spectrum can be used, transferred, and otherwise manipulated as a commoditized object or entity. Conventionally, spectrum has been allocated principally in terms of area, time, and frequency. FIG. 1 is a schematic graph of blocks of conventional spectrum use rights that may be transferred from a corresponding spectrum holder to a spectrum user. The components that identify a block of spectrum include a time window, a frequency-based spectral mask, a geographic coverage area, and/or a transmitted power limit, which may be combined to form a spectrum commodity object 10. The graph of FIG. 1 schematically illustrates blocks of spectrum in three dimensions, including time, space (or geographic coverage area) and frequency. Each spectrum commodity object 10 also may have the associated transmitted power limit, which is a power value that radios operating in accordance with the transmitted power limit may not exceed. Each spectrum commodity object 10 may be associated with use rights that may be transferred from a corresponding spectrum holder to a spectrum user in the secondary market. The spectrum commodity object may have an associated monetary or non-monetary value, or may not be associated with a value.
In today's advanced wireless networks, cognitive radios are available that have the capability to dynamically tune to different frequencies. Even when radios have such capabilities, however, in most cases these wireless radios still are initially configured to use a specific frequency that is available at the time of such initial configuration. Accordingly, a cognitive radio, although as a technical matter may be capable of using many different frequencies, is still being statically configured to use a specific frequency. The radio, therefore, typically will utilize the specific frequency of the initial configuration regardless of future conditions that might negatively affect performance while using the statically assigned frequency, and regardless of the technical capability of dynamically changing to a different frequency that may offer better performance. The reason for statically configuring otherwise cognitive radios in this manner is mostly due to the fact that a single device in a network does not have enough information about network-wide spectrum allocation to make a dynamic decision to move to a different frequency that may offer better performance without creating interference issues with other user devices. Thus, while a spectrum user device as a technical matter may be able to determine that the currently configured spectrum is not offering satisfactory performance, the device essentially would not know what other spectrum is currently available, or how many devices are already using the other available spectrum so as to avoid interference issues. To determine spectrum that would offer enhanced performance, a cognitive radio would need to “know” how the spectrum is being allocated and used by other devices in or near the coverage area of the user device.
Some spectrum user devices have a sensing capability. In particular, such sensing devices may attempt to sense congestion and interference at a frequency of usage. If performance due to congestion and interference deteriorates below an acceptable level, the sensing user device may attempt to determine a more suitable frequency that offers improved performance, and then retune to a more suitable frequency if one can be identified. This device-based sensing capability, however, often proves incomplete and deficient. Sensing devices typically lack the full capability to perform sufficient detection and analysis of all usages by potentially interfering devices in or near the pertinent coverage area. Accordingly, even the operation of a sensing device will not ensure adequate performance because device sensing capabilities are limited. In addition, sensing devices conventionally do not share sensed information with other sensing devices. In this regard, difference devices or categories of usage may employ different formats and metrics for processing sensing data, and therefore the sharing of sensing information among spectrum user devices is substantially limited.
Furthermore, not all spectrum user devices possess even a limited sensing capability. Non-sensing devices, therefore, are unable to determine a more suitable frequency of operation to overcome congestion and interference issues.
In view of the above deficiencies of conventional networks, cognitive radio capabilities are not being utilized to their full potential, insofar as cognitive radios conventionally have been configured to operate only at a specific frequency (or limited frequencies) set by an initial configuration, and lack full sensing capabilities to determine spectrum usage among the various user devices within a pertinent coverage area.